1. Field of the Invention
The present invention relates to a scanning-line interpolating circuit, a scanning-line interpolating method and an image display device, and more particularly to the scanning-line interpolating circuit and the scanning-line interpolating method to be used for the scanning-line interpolating circuit, and an image display device provided with the scanning-line interpolating circuit, which are employed in such a case in which, in display devices including plasma display panels, liquid crystal display devices, cathode-ray tubes using a progressive scanning method, and a like, when a video input signal is converted from an interlaced scanning signal to a progressive scanning signal, a correlation is judged among pixel data on a plurality of pixels located in vertical and oblique directions and, based on the result from the judgement, interpolated pixels are generated.
The present application claims priority of Japanese Patent Application No. 2005-245978 filed on Aug. 26, 2005, which is hereby incorporated by reference.
2. Description of the Related Art
When a video input signal such as a television signal is converted from an interlaced scanning-line signal to a progressive scanning-line signal, in the case of motion video signals, there is a weak correlation among data blocks during each field and, therefore, interpolation on the motion video signal is performed by using information having a strong correlation among the data blocks during the same field. In such a situation, if the interpolated signals are produced only based on a mean value of pixel data blocks on up and down scanning lines which sandwiches an interpolating pixel on a scanning line for interpolation, when a slanting line is displayed on a display screen, edges of the slanting line are jagged, that is, “jaggies” occur on an image to be displayed. Various scanning-line interpolating methods are proposed to reduce such “jaggies” on slanting lines on the display screen.
One example of such scanning-line interpolating methods is a slanting correlation adaptive-type of scanning-line interpolating method.
In the slanting correlation adaptive-type scanning-line interpolating method, for example, as shown in FIG. 1, it is here assumed, to explain the conventional method, that a pixel A(0) corresponding to an interpolating pixel X on a K−1st scanning line (on a video input upper line) located above the K-th (“K” is an integer of 2 or more) scanning line on which the interpolating pixel X (interpolating pixel X) exists, pixels A(−1), A(−2), A(−3), . . . , and A(−N) (“N” is a positive integer) arranged in order approaching the pixel A(0) occurring on a left side of the pixel A(0) on the K−1st scanning line, and pixels A(1), A(2), A(3), and A(N) arranged in order approaching the pixel A(0) existing on a right side of the pixel A(0) on the K−1st scanning line are provided. It is also assumed that a pixel B(0) corresponding to the interpolating pixel X on the K+1st scanning line (on a video input lower line) located below relative to the interpolating pixel X, pixels B(−1), B(−2), B(−3), . . . , and B(−N) (N is a positive integer) arranged in order approaching the pixel B(0) occurring on a left side of the pixel B(0) on the K+1st scanning line and pixels B(1), B(2), B(3), . . . , B(N) arranged in order approaching the pixel B(0) occurring on a right side of the pixel B(0) on the K+1st scanning line are provided.
According to the conventional technology, an absolute value of a difference between data on a pixel A(0) located upward relative to the interpolating pixel X and data on a pixel B(0) located downward relative to the interpolating pixel X, an absolute value of a difference between data on a pixel A(m) (“m” is a positive integer) located in an oblique direction relative to the interpolating pixel X and data on a pixel B(−m) also located in an oblique direction relative to the interpolating pixel X and an absolute value of a difference between data on a pixel A(−m) in other oblique direction relative to the interpolating pixel X and data on a pixel B (m) in the other direction relative to the interpolating pixel X are compared with one another and it is judged from results from the comparison that there is a strong correlation in the direction in which the smallest absolute value is obtained. In this case, when there is a strong correlation in up-and-down directions, a mean value of pixel data on the pixel A(0) and the pixel B(0) is defined as pixel data to be used for interpolation of the pixel to be interpolated X. Also, when there is a strong correlation in the oblique direction and when an absolute value of a difference in pixel data between the pixel A(m) and pixel B(−m) is the smallest, a mean value of pixel data of the pixel A(m) and pixel A(−m) is defined as pixel data to be used for interpolation of the interpolating pixel X. Furthermore, when there is a strong correlation in the oblique direction and when an absolute value of a difference in pixel data between the pixel A(−m) and the pixel B(m) is the smallest, a mean value of pixel data of the pixel A(−m) and the pixel B(m) is defined as pixel data to be used for interpolation of the interpolating pixel X. By using the above definition and comparison, jaggies on slanting lines are reduced.
Conventional technologies of this type are disclosed in the following Patent References. FIG. 2 is a block diagram showing electrical configurations of a conventional scanning-line interpolating device (circuit) disclosed in Patent Reference 1 (Japanese Patent Application Laid-open No. 2003-18397, Page 3, FIG. 12). The disclosed scanning-line interpolating device, as shown in FIG. 2, includes a one-line delay circuit 1, one-pixel delay circuits 11, 12, 13, 14, 15, 16, and 17, one-pixel delay circuits 21, 22, 23, 24, 25, 26, and 27, difference absolute value calculating circuit 31, 32, 33, 34, 35, 36, and 37, mean value calculating circuits 41, 42, 43, 44, 45, 46, and 47, a minimum value detecting circuit 48, and an interpolating signal selecting circuit 49.
In the conventional scanning-line interpolating device (circuit), a video input signal “in” being an interlaced scanning signal is input through the one-line delay circuit 1 sequentially to the one-pixel delay circuits 11, 12, 13, 14, 15, 16, and 17 and is directly input sequentially to the one-pixel delay circuits 21, 22, 23, 24, 25, 26, and 27. Then, pixel data of each of the pixels A(−3), A(−2), A(−1), A(0), A(1), A(2), and A(3) to be supplied to the K−1st scanning line is output from the one-pixel delay circuits 11, 12, 13, 14, 15, 16, and 17. Also, pixel data of each of the pixels B(−3), B(−2), B(−1), B(0), B(1), B(2), and B(3) to be supplied to the second scanning line is output from the one-pixel delay circuits 21, 22, 23, 24, 25, 26, and 27.
The pixel data blocks of each of the pixels A(3), A(2), A(1), A(0), A(−1), A(−2), A(−3) and each of the pixels B(−3), B(−2), B(−1), B(0), B(1), B(2), and B(3) are input respectively to the difference absolute calculating circuits 31, 32, 33, 34, 35, 36, and 37, and absolute values of each difference between the pixel on the upper scanning line and the pixel on the lower scanning line |A(−3)−B(3) |, |A(−2)−B(2) |, |A(−1)−B(1) |, |A(0)−B(0) |, |A(1)−B(−1) |, |A(2)−B(−2) |, and |A(3)−B(−3) | are output from the difference absolute calculating circuits 31, 32, 33, 34, 35, 36, and 37.
The pixel data blocks of each of the pixels A(3), A(2), A(1), A(0), A(−1), A(−2), and A(−3) and each of the pixels B(−3), B(−2), B(−1), B(0), B(1), B(2), and B(3) are input respectively to the mean value calculating circuits 41, 42, 43, 44, 45, 46, and 47, and mean values [A(−3)+B(3)]/2, [A(−2)+B(2)]/2, [A(−1)+B(1)]/2, [A(0)+B(0)]/2, [A(1)+B(−1)]/2, [A(2)+B(−2)]/2, and [A(3)+B(−3)]/2 are output. A minimum value of the above absolute values of the above differences is detected by the minimum value detecting circuit 48 and an output from each of the mean value calculating circuits 41, 42, 43, 44, 45, 46, and 47 corresponding to a pair of pixels existing in the direction and at the angle where the minimum value is detected by the minimum value detecting circuit 48 is selected by the interpolating signal selecting circuit 49 and is output as pixel data to be used for interpolation of the interpolating signal x.
Moreover, in the scanning-line interpolating device disclosed in Patent Reference 2 (Japanese Patent Application Laid-open No. 2002-185934, Page 10, FIG. 1), an interpolating signal is produced by an interpolating signal producing means by blending a value for interpolation in an oblique direction with a value for interpolation in up-and-down directions. That is, when a difference value of pixel data between pixels occurring in an oblique direction relative to an interpolating pixel is between a first value and a second value, a value of the interpolating pixel is calculated by using the first interpolating value obtained by using pixels occurring in a vertical direction and a second interpolating value obtained using pixels occurring in an oblique direction and, therefore, smooth interpolating process is performed in an image containing edges in an oblique direction.
However, the conventional scanning-line interpolating devices as described above have the following problems. That is, in the conventional scanning-line interpolating device as shown in FIG. 2, a minimum value of an absolute value of a difference is detected by the minimum value detecting circuit 48, however, if information about an angle of an oblique line increases, in some cases, a minimum value obtained in a direction being reverse to a direction in which a minimum value is detected is employed in an actual interpolating processing and, as a result, erroneous judgement is made, which causes a flicker, bright point, dark point, or a like to occur on a display screen.
Also, the scanning-line interpolating device disclosed in the Patent Reference 2 has a problem in that, since data for interpolation in up-and-down directions and data for oblique directions are blended, one half the effectiveness of interpolation in the oblique direction is lost. Moreover, if the data for the interpolation in up-and-down directions and data for the interpolation in the oblique direction are not blended at all, when an interpolating signal obtained by judgement for interpolation in the oblique direction and an interpolating signal obtained by judgement for interpolation in the up-and-down directions are adjacent to each other, the obtained interpolating curve is not smooth, which causes pseudo-edges to occur and a display screen to be unnatural.
FIG. 3 is a diagram showing effects of interpolation performed by the conventional scanning-line interpolating device disclosed in the Patent Reference 2 and shown in FIG. 2, in which pixel numbers are plotted as abscissa and pixel data as ordinate. In FIG. 3, an “upper line” shown by a broken line represents an interlaced scanning signal to be supplied to the K−1st scanning line. A “lower line” shown by a broken line represents an interlaced scanning signal to be supplied to the K+1st scanning line. Other broken lines represent interpolating signals produced by using the interlaced scanning signal to be supplied thereto. An “up-and-down interpolating line” shown by a broken line is plotted by using mean values of pixel data blocks at two points using pixels located in a vertical direction on the upper and lower lines being symmetric with respect to a point of the interpolating pixel X. A “slanting 45° interpolating line” shown by a broken line is plotted by using mean values of pixel data blocks at two points using pixels out of three pixels, each being a square pixel, located in an oblique direction on the upper and lower lines being symmetric with respect to a point of the interpolating pixel X. A “slanting 15° interpolating line” shown by a broken line is plotted by using mean values of pixel data blocks at two points using pixels existing in an outermost place out of 11 pixels, each being a square pixel, located on the upper and lower lines being symmetric with respect to a point of the interpolating pixel X. A “blend interpolating line” shown by a broken line is plotted by using a mean value of pixel data blocks obtained by data for the up-and-down interpolation and data for the slanting 15° interpolation. The slope of the blend interpolating line becomes gentle compared with that of the slanting 15° interpolating line which shows a problem in that one half the effectiveness of the interpolation in an oblique direction is lost when compared with the case of using only the slanting 15° interpolation. The problems to be solved by the present invention includes the problems described above as examples.